FB25 is a new-generation engine by the Subaru brand, first produced in 2010. It is a 2.5L non-turbo boxer 4-cylinder motor, meant to substitute EJ25 in Subaru Legacy and Forester.
Being a more powerful modification of FB20, this motor features a great number of new technologies and innovations. It has an aluminum cylinder block and identical stroke, but 94 bore cast iron sleeves contribute to greater displacement. Cylinder walls are 3.5 mm thick. To decrease friction inside the block and lessen the compression index to 10.0:1, Subaru utilized restyled pistons.
FB25 Engine Specs
|Manufacturer||Gunma Oizumi Plant|
|Also called||Subaru FB25|
|Cylinder block alloy||Aluminum|
|Configuration||Flat-4 (Boxer engine)|
4 valves per cylinder
|Piston stroke, mm (inch)||90 (3.54)|
|Cylinder bore, mm (inch)||94 (3.70)|
|Displacement||2498 cc (152.4 cu in)|
|Power output||127 kW (172 HP) at 5,800 rpm
129 kW (175 HP) at 5,800 rpm
|Torque output||236 Nm (174 lb·ft) at 4,100 rpm
235 Nm (173 lb·ft) at 4,000 rpm
|HP per liter||68.9
|Weight, kg (lbs)||–|
|Fuel consumption, L/100 km (mpg)
|Subaru Forester 2.5
|Oil consumption, L/1000 km
(qt. per miles)
|up to 1.0
(1 qt. per 600 miles)
|Recommended engine oil||0W-20, 5W-20, 5W-30, 5W-40|
|Engine Oil Capacity, L (qt.)||4.8 (5.1)|
|Oil change interval, km (miles)||5,000-10,000
|Normal engine operating temperature, °C (F)||–|
|Engine lifespan, km (miles)
-No life span loss
FB motors keep aluminum heads (DOHC with 4 valves per cylinder), containing cylinder head and camshaft carrier, which decreases the thickness and mass of metal. Lifters are replaced by roller rocker arms. Intake and exhaust camshafts feature AVCS, a variable valve timing system. After equipping cylinder heads with fuel injectors, the engine became more powerful though the injection system is rather intricate.
To achieve higher airflow, Subaru restyled intake and exhaust valves and ports. Every FB25 motor is equipped with maintenance-free timing chains. Changes in exhaust system concerned fresh manifolds and diameters of tubes for more efficiency and catalytic converter warming-up improvement.
In 2014, some minor changes were made. Cylinder walls became thinner (3.2 mm) and fresh pistons were utilized to reach a higher compression index of 10.3:1. Heads gained restyled intake ports and other intake valves of 36 mm. Besides, the intake manifold and exhaust system were subjected to updates.
In comparison with EJ25, FB25 is more responsive at low speeds. Having an identical output, it achieves lower rpm and higher torque at lower rpm. Moreover, it consumes less fuel. As a result, FB25 turns out to have more benefits.
- 2011+ North American Subaru Forester
- 2013+ North American Subaru Legacy
Subaru FB25 Engine Problems and Reliability
- Carbon build-up
- Oil consumption
- Cam carrier seal leak
This engine has average reliability ratings, according to us. You may even make a good case for above-average dependability. However, expensive cam carrier seal oil leaks and potential oil usage issues bring down the FB25’s reliability somewhat.
Unfortunately, oil use appears to have a much smaller impact on engines. If oil consumption is bad enough, the manufacturer offers a TSB for new rings or short-blocks. We won’t hold carbon build-up against the FB25. Many modern engines utilize DI and its truly incredible technology. Carbon build-up is just a minor disadvantage.
Maintenance, in particular regular maintenance and luck of the draw, are important factors in determining Subaru FB25 dependability. All engines have a few rotten apples, and we just can’t change that. However, taking good care of your engine is a simple approach to boost the chance of having a trouble-free experience with the flat-4 boxer engine.
Is Subaru FB25 An Interference Motor?
Yes, FB25 is an interference motor. All Subaru engines since 2010 are interference.
Is The Subaru FB25 Engine Good?
The engine runs well and is durable, with a lifespan of 200,000 miles. Unfortunately, the FB25 engine was not designed to be built aggressively. It would only exacerbate an already outstanding engine. It has good power, but if you’re not happy with the amount of power it produces, you can purchase a Subaru WRX instead. However, if you simply want to increase engine durability, you may install an aftermarket cat-back exhaust system and modify the ECU. This may improve performance while also increasing reliability and horsepower by about 190 units.